A fuel injector for injecting fuel into a combustion engine comprises a valve that can be opened by means of an electrically driven actuator against the force of a spring. Different designs are known in the art, comprising electromagnetic or piezo actuators, digital or servo models and actuators for different fuel types such as gasoline or diesel.
US 2006/0255185 A1 shows a fuel injector with electromagnetic actuator in which the valve comprises a needle and the valve opens when the needle is moved in a direction of a nozzle of the injector.
An amount of fuel running through the injector is generally dependent on the time the actuator is driven. A flow curve that shows a relationship between the drive time and the throughput has generally three successive areas. Very short drive times relate to a ballistic area where the needle is never fully open and the injection is never fully stabilized. Nevertheless, flow rates are generally repeatable. With longer drive times, the injector will be in a non-linear area. In this area, the needle reaches full opening but the flow dynamics are not stabilized as not all parts of the injector had enough time to settle. With even longer drive times, a linear area is entered, where the needle reaches its fully open position, the flow is stabilized and all the moving parts of the injector have settled.
The smaller the non-linear area is, the smaller are part-to-part and shot-to-shot deviations. An ideal flow curve would be monotonic with only a ballistic area and a linear area.
In order to help the needle to mechanically settle during an opening phase, a hydraulic dampening area may be foreseen that provides hydraulic dampening. However, extensive dampening leads to slower opening transients and much slower closing transients, which is undesirable.